Joseph Labrum spent his summer internship building components to upgrade an experiment that successfully compared physical objects without learning anything about the objects themselves. Such a “zero-knowledge protocol” system is a promising first step toward a technique that could possibly be used in future disarmament agreements, pending the results of further development, testing, and evaluation. While important questions remain, it might have potential application to verify that nuclear warheads are in fact true warheads without revealing classified information. (See article, “PPPL and Princeton demonstrate novel technique that may have applicability to future nuclear disarmament talks.”)

Labrum is a senior at the University of California-Berkeley studying nuclear engineering. He helped create a precise device for counting the bubbles in detectors used in the experiment by working with Sébastien Philippe, a graduate student at the Princeton University Department of Mechanical and Aerospace Engineering, and Robert Goldston, a fusion scientist, professor of astrophysical sciences at Princeton and former director of the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL).

“The idea is to have better statistics, better accuracy, for the next phase of our zero-knowledge experiments” said Philippe, lead author of a paper published in Nature Communications in September that described the original system. “This is very important work to be able to detect smaller and smaller changes in objects that are not that different from each other,” he said of the improved method for counting bubbles. Coauthors of the paper together with Goldston were Alex Glaser, associate professor in Princeton’s Woodrow Wilson School of Public and International Affairs and the Department of Mechanical and Aerospace Engineering, and Francesco d’Errico, senior research scientist at the Yale University School of Medicine and professor at the University of Pisa, Italy.

The device Labrum assembled can be remotely operated, allowing two different parties to view the number of bubbles in the detectors, Goldston said. And using a series of photos or “movies” for tracking the bubbles could produce a more accurate count. “The problem is bubbles tend to hide behind each other,” Goldston said. “We need to develop a better method to measure how many bubbles in this bubble counter.

Labrum was one of 23 Science Undergraduate Laboratory Internship (SULI) students at PPPL this summer in a program sponsored and managed by the DOE Office of Science's Office of Workforce Development for Teachers and Scientists. He plans to present a poster on his project at the American Nuclear Society Winter Meeting and Nuclear Technology Expo to be held in Las Vegas in November.

Building a bubble-counting device

Working from Philippe’s designs, Labrum fitted a small optical table inside a bread-box-sized container. He then installed a turntable that rotated a collection of tubes filled with Yale-created bubble detectors. The bubbles form when high-energy neutrons interact with a specially designed mixture of fluids filling the detectors.

Labrum next connected a light, along with a mirror and a diffuser, to shine light evenly onto the bubble detector. He positioned a camera to take high-quality images of the bubbles as the turntable rotated. Connected to the camera is a small credit-card size computer that collects and analyzes data recorded by the detectors resulting from the neutrons interaction with a variety of objects.

Labrum also worked on a computer program that would count the number of bubbles by pinpointing the center of each one. When the program is completed, the goal is to accurately count 1,000 bubbles per vial, about 10 times more than the current capability, according to Philippe.

The coding was challenging. “I am not a coder,” Labrum said. “That kind of coding was not in my skill set prior to the internship.” He got up to speed by reading articles provided by Philippe and Goldston.

Philippe said researchers chose Labrum to work on the project because he was a nuclear engineering major who had already garnered a lot of experience at laboratories. “Joe was a very good fit,” Philippe said. “He had a natural sense of how to build practical, useful systems, while understanding the theory behind it.” “He did a beautiful job putting together this instrument,” Goldston said.

Returning to N.J. for internship

A native of North Hanover, a small town in Burlington County, New Jersey, Labrum said he enjoyed being back home with his family for the summer during his internship. “Being home and being at one of the best labs in the world was pretty nice,” he said.

Labrum learned about nuclear engineering in a middle school class on careers. He became interested in nuclear non-proliferation in a college class on “analytical methods to non-proliferation.” As a sophomore, he worked at Lawrence Berkeley National Laboratory on a computer code that modeled radiation from a decommissioned reactor in Baghdad, Iraq. Last year, he worked with researchers at the National Ignition Facility at Lawrence Livermore National Laboratory on the redesign of a soft X-ray imaging camera that was used as a diagnostic tool.

Labrum said he would encourage other students to apply for the SULI internship and to take full advantage of the experience when they’re here. “It’s definitely very rewarding,” he said. “You should meet as many people as you can when you’re at PPPL because you’re surrounded by some of the most talented people in the field.”

The next step for Labrum will be applying for graduate schools to get his Ph.D. in nuclear engineering. He hopes he might return to Princeton as a graduate student. Meanwhile, he and Goldston have discussed a new mathematical approach to counting the bubbles in detectors that might someday play a role in verifying future arms control agreements.

“Nuclear disarmament is a big thing,” Labrum said. “The world should strive to control the amount of nuclear weapons and know how many each country has and limit each country.”

Seed money for the original research came to Princeton from The Simons Foundation of Vancouver, Canada, through a nonprofit called Global Zero, and from the U.S. Department of State Verification Assets Fund.

PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Established by Congress in 2000, NNSA is a semi-autonomous agency within the U.S. Department of Energy responsible for enhancing national security through the military application of nuclear science. NNSA maintains and enhances the safety, security, and effectiveness of the U.S. nuclear weapons stockpile without nuclear explosive testing; works to reduce global danger from weapons of mass destruction; provides the U.S. Navy with safe and effective nuclear propulsion; and responds to nuclear and radiological emergencies in the U.S. and abroad. Visit nnsa.energy.gov for more information.